Pfizer on Monday said it will buy cancer drug developer Trillium Therapeutics in a $2.26 billion deal. Pfizer, which acquired a $25 million stake in Trillium last year, will buy the remaining shares for $18.50 apiece, representing 203.8% premium on the stock's last closing price. Pfizer's oncology portfolio includes 24 approved drugs that yielded about $10.9 billion revenue in 2020.